The present invention relates to hole formation in turbine components and more specifically to the formation of an overhanging tab on the upstream portion of the discharge end of a film hole using an additive manufacturing process.
Airfoils in a turbine engine often include cooling holes for discharging a film of cooling air along the outer surface of the airfoil to affect film cooling. These may be referred to as “film cooling holes” or “film holes.”
Generally, cooling holes extend through a wall in an aircraft component from an entry end to an exit end. In some cooling holes, the exit end is configured as a generally conical diffuser and is positioned in a surface of an aircraft component that has a leading edge and a trailing edge. It is sometimes desirable that instead of being conical, the diffuser section of a cooling hole be configured such that the upstream side overhangs the exit. In this regard, flow through the cooling hole as it nears the exit side of the cooling hole is turned to be closer to tangential to the local hot gas surface being protected by the film cooling. The flow in the exit end of the cooling hole is turned such that the flow is more parallel to the surface to which the exit end of the cooling hole discharges.
To cause this turn in flow, an overhanging tab is positioned at the leading edge of the exit end of the cooling hole. The overhanging tabs are configured such that they extend toward the trailing edge of the cooling hole exit. Such overhanging tabs can be very thin and therefore are difficult to make using conventional means.
Conventional methods for forming film cooling holes include casting and machining. One problem with film holes produced by conventional methods is that they are limited with regard to thinness. In this regard, some conventional methods are incapable of forming thin overhanging tabs in that edges formed by these methods have a minimum radius and that minimum radius is greater than that desired for the overhanging tabs. While some conventional methods are capable of forming overhanging tabs with the desired thin edge, they are not capable of producing such overhanging tabs with the desired consistent thickness and sufficient size.